1. Technical Field
The present disclosure relates to the electronic memories domain and more specifically to a memory structure with an access transistor (TR) connected in series with a programmable resistive element.
2. Description of the Related Art
Programmable electronic memories for a number of years have undergone significant development, in particular with the growth of non-volatile memories which keep the information even when they are not powered and which are widely used in portable electronic devices.
It is desirable to integrate those non-volatile memories into integrated circuits comprising CMOS logic in order to realize full systems (called “system on chip” in the Anglo Saxon literature), including in a same semiconductor product, electronic logic and memory circuits.
The category of non-volatile memories subdivides in three sub-categories, that is rewritable ROM memories (Read Only Memory including PROM, EPROM, EEPROM, and FLASH memories), non-re-writable ROM memories, and memories called RAM (Random Access Memory).
Research regarding RAM memories has enabled the development of ferroelectric-type memories (FeRAM) and magneto resistive memories (MRAM), the latter based on a resistive material controlled by a magnetic field and, more recently, phase change memories (PCM in the Anglo Saxon literature).
Phase change memories (PCM) are based on the use of chalcogenide alloys (Ge2, Se2, Te2) which present two possible phases, respectively disorderly (amorphous) or more orderly (crystalline), distinguished from one another by different resistivity. The transition from one phase to another is controlled by a cycle of heating/cooling and enables then to fix the material in a predetermined phase representative of a given information, a “0” or a “1”.
U.S. Pat. Nos. 3,271,591 and 3,530,441 describe the use of phase change material (PCM) to realize programmable memory elements.
Another known technique allowing realization of a programmable resistive memory element is based on the use of a solid electrolyte and the dissolution of metal in the electrolyte using a current or an electric field. The international application WO 2005/124788 entitled “Nanoscale Programmable Structures and methods of forming and using the same” from M. KOZICKI, illustrates such a technique of realization of a programmable memory cell.
The use of techniques outlined above has interesting advantages because of significant space savings offered by the memory cell which may be formed with one access transistor. Drawbacks remain, in particular related to the high number of photolithography steps used by these techniques.
For these reasons in particular, alternative techniques to achieve cells and memory circuits based on programmable resistive elements are the subject of much research.